This is a study of human females exposed to radiation when they were in utero, with comparable unexposed matched controls, now being followed during their young adult and reproductive years. The overall objective is to find out whether radiation doses received by female fetuses when their mothers had diagnostic x-ray procedures (pelvimetry and other, 1947-1952) may have produced any effects that could now be observed. Animal experiments indicate that some fetal tissues are very sensitive to radiation damage, especially the gonads and the central nervous system. The study goal is to determine whether any observed differences between exposed and control women are independently related to radiation exposure during fetal life. As previously reported, Phase I of the study showed a 10-15 percent increase in fertility in exposed women early in their reproductive lives. The difference remained statistically significant after adjustment for differences in economic, social, and medical factors. Preliminary analysis of Phase II data, obtained from direct follow-up of exposed-control pairs who are now aged 22-28, showed that exposed-in-utero women had 15 percent more total pregnancies than controls in 1960-1969, and 7 percent more in 1970-75. Exposed and control women are similar in number of siblings, number of children wanted, contraceptive use, and frequency of therapeutic abortion. Other findings suggest possible exposed-control differences in growth, development, and behavior. Exposed women have completed fewer grades of school, have poorer general health, more menstrual problems, more of certain diseases and accidents, and are heavier for height than controls. BIBLIOGRAPHIC REFERENCE: Meyer, Mary B., J.A. Tonascia, T. Merz. Long-term effects of prenatal x-ray on development and fertility of human females. In Proceedings of the IAEA Symposium on Biological Effects of Low Level radiation Pertinent to Protection of Man and His Environment. Chicago, Ilinois, USA, 3-7 November, 1975.